Why the long face? Well, because people trust them, particularly in troubled times, says research suggesting long-faced people are seen as natural leaders.

Homing in on facial cues that suggest tallness, as long faces do, is thought to have evolved from ancestral times when survival depended on choosing the right leader. "Our results suggest we turn towards the most dominant-looking people for leadership, especially when we are faced with a threat," says the psychologist Daniel Re of the University of St Andrews, who led the study.

Height has long been associated with success. In the last century, the taller of the two candidates won most US presidential elections.

In the research, reported in the journal Evolutionary Psychology, volunteers were presented with pictures on a screen of the faces of men and women whose features could be manipulated to make them appear taller or more masculine. They were then told to use the computer to transform the picture to resemble someone they would like to lead their country in peacetime and war.

When looking for a peacetime leader the apparent length was increased by 6 per cent in men's faces and stayed the same for women. But for war, the apparent length was increased by 34.9 per cent in female faces and 45.8 per cent in male ones.

Of course the assumptions made about the leadership qualities of people with long faces can be wide of the mark. While Tony Blair, Britain's longest-serving post-war prime minister stands 6ft in his socks, he has a face that makes him seem short. And then there is the anomaly of Nicolas Sarkozy, who has a long face, but is rather short at 5ft 5in.

The researchers said conclusions were harder to reach with female politicians, as hairstyles can make the face look rounder. Margaret Thatcher had a slightly rounder face (short-looking) but was actually 5'6" in her prime. Among other prominent women, the Duchess of Cambridge is an example of someone who has a rounder face but is actually 5'8", around the average male height. "These results could be troubling for political scientists," say the researchers. "They suggest that leadership choices are affected by face cues irrelevant to political expertise."